April 30 (UPI) -- Apes had adapted to the ground by the time the earliest humans emerged, according to a new study. Life on the ground, researcher Thomas Prang determined, preceded human bipedalism.
The human body is uniquely adapted for the task of walking and running, the result of a variety of evolutionary factors. The human foot is especially unique, boasting a big toe that lacks ape-like gripping abilities but having a full arch that offers spring-like energy.
But how did humans evolve their feet? Which ape species did they borrow from? Now, scientists have some answers.
"Our unique form of human locomotion evolved from an ancestor that moved in similar ways to the living African apes -- chimpanzees, bonobos, and gorillas," Prang, a doctoral candidate in biological anthropology at NYU, said in a news release. "In other words, the common ancestor we share with chimpanzees and bonobos was an African ape that probably had adaptations to living on the ground in some form and frequency."
To better understand what the earliest common ancestor of humans and chimpanzees might have looked like, Prang studied the relationship between locomotion and the morphology of primate foot bones. Prang also closely analyzed the morphology of Ardipithecus ramidus -- or "Ardi" -- a 4.4 million-year-old human ancestor from Ethiopia.
Prang's research showed the apes from which the earliest humans evolved had already adapted to life on the ground and adopted some of the features that would prove essential to human bipedalism.
"Therefore, humans evolved from an ancestor that had adaptations to living on the ground, perhaps not unlike those found in African apes," Prang said. "These findings suggest that human bipedalism was derived from a form of locomotion similar to that of living African apes, which contrasts with the original interpretation of these fossils."
Previous interpretations of Ardi foot bones suggested the early species' foot was more monkey-like than it was similar to the feet of chimpanzees or gorillas. Such an interpretation suggested many of the traits shared by chimpanzees, bonobos, gorillas and orangutans evolved independently.
Conversely, Prang's work, published this week in the journal eLife, suggests the morphology underlying human bipedalism has deep evolutionary roots -- roots shared by humans' primate relatives.
"Humans are part of the natural world and our locomotor adaptation -- bipedalism -- cannot be understood outside of its natural evolutionary context," Prang said. "Large-scale evolutionary changes do not seem to happen spontaneously. Instead, they are rooted in deeper histories revealed by the study of the fossil record."